This study consists of 2 parts: 1) a treatment phase, and 2) a monitoring phase. In the treatment phase, participants will be randomly assigned to 1 of 4 groups: a low or high dose rhEPO treatment group or low or high dose placebo group (control group). All other aspects of treatment during the acute post-injury phase will follow the standard treatment protocol for individuals with severe TBI. Generally the treatment phase lasts 1-2 weeks or the amount of time that is required for patients to receive treatment of their TBIs in the ICU (intensive care unit). The monitoring part of the study (which includes recording information from tests performed as part of the standard TBI treatment, as well as some additional tests performed especially for the study) lasts for up to 6 months after the TBI.